A squib is a small explosive about the size of a firecracker. It is often used to ignite a larger pyrotechnic explosive, such as a rocket engine.

In aviation squibs are used to generate pressurised gas to open valves and operate small mechanical devices on such as ejection seats and to pierce metal diaphrams that are retaining pressurised liquids such as halon and fluorocarbon extinguishants or release compressed nitrogen gas to act as a propellant.

They are also widely used in the special effects industry to simulate a bullet hit on a person by coupling the squib itself with a packet of either fake blood or dust/debris.

A "damp squib" is literally one that fails to go off due to wetting but the term has come into general use to mean anything that fails to meet expectations.